Method and apparatus for permissive control of a mast and grapple

ABSTRACT

A method and apparatus for the permissive control of a mast and fuel grapple to be used in the movement of reactor fuel components, including fuel assemblies, single blade and double blade guides, to be used in a Boiling Water Reactor (BWR) nuclear reactor. The Permissive Control System reduces the chance of human error associated with the movement of reactor components by assisting in controlling the location (plant coordinate) of the mast for picking-up and dropping-off reactor components, the sequence of reactor component movements, the orientation (angular rotation) of the mast and fuel grapple, the raising and lowering of the grapple, and the opening and closing of the fuel grapple.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. patent application is a Divisional application of, and claimspriority under 35 U.S.C. §120 to U.S. application Ser. No. 11/984,276,filed on Nov. 15, 2007, the entire contents of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Example embodiments relate in general to a method and apparatus forcontrol of the three-dimensional movement of a mast. More specifically,example embodiments relate to control of the movement of nuclear reactorcomponents, in terms of ensuring that their two-dimensional location(i.e., plant coordinate), their elevation, and their orientation (i.e.,angle of rotation) correspond to a reactor engineer's instructions.Example embodiments further relate to a control permissive that allowsreactor components to be picked-up and dropped-off in plant coordinatesand orientations that match a reactor engineer move sheet during nuclearreactor refueling or initial start-up.

2. Related Art

In a Boiling Water Reactor (BWR) the orientation of reactor componentssuch as fuel assemblies and blade guides (single or double blade) isimportant for various reasons. During operation of the reactor the fuelassemblies must be oriented for proper physics of the core. Duringmaintenance and examination, single and double blade guides may beoriented to keep control rods in a vertical position while providingaccess for inspection.

Fuel assemblies and single blade guides may have four possibleorientations (each at and angle of rotation of 90° increments) when theyare lowered into the core or spent fuel pool. In addition to theorientation of the fuel assembly, another important consideration may bethe location of the channel fastener. Fuel assemblies may be located ina quadrant of a fuel cell, and the fasteners must face the center of thecell. The single blade guide also has an orientation consideration, asbuttons on the side of the blade must face the control rods in order forthe blade to effectively hold the rods in a vertical position followingplacement of the blade into a cell. A double blade guide can be loadedin only two directions, depending on the maintenance or examinationbeing conducted in the core.

Mis-orientation of reactor components may be a potentiallytime-consuming and expensive problem in the operation of nuclearreactors. Most US nuclear plants classify a fuel assembly in the wrongorientation as a fuel handling error, if the wrong orientation is in thecore. A fuel handling error could cost a utility $1.5 M on critical pathtime. Conventionally, the responsibility of fuel assembly orientationhas been on human operators called the fuel mover and the spotterpositioned on a refueling platform, to ensure that reactor componentsare relocated and oriented according to plant move sheets. Even with asecond or third verifier, reactor components may be installed in thewrong orientation, leading to plant downtime or even serious reactormalfunction, potential accidents, and potential Nuclear RegulatoryCommission (NRC) fines and investigation.

SUMMARY OF INVENTION

A boiling water reactor requires movement of reactor components (fuelassemblies and single/double blade guides) during plant refueling andplant initial start-up. The movement of these components occurs betweenthe reactor core and spent fuel pool. Conventionally, during plantrefueling ⅓ of the fuel assemblies may be substituted with new fuelassemblies while another ⅔ of assemblies may be repositioned within thereactor core. During initial plant startup, the entire reactor core isfilled with fuel assemblies. In either a refueling or initial startupscenario, a significant movement of reactor components may occur as fuelassemblies and blade guides are picked-up and dropped-off whiletraveling through a flooded “cattle chute” that may connect the reactorcore and the spent fuel pool. The Permissive Control System assists inpreventing the physical extraction or insertion of reactor components ifthe mast and grapple are not in the correct location or orientation, andthe Permissive Control System may provide an error message to a user oroperator, as opposed to relying on human verification to identifymisplaced or mis-oriented components.

A telescoping mast with a grapple on the end is provided to move thereactor components and rotate them into the proper orientation. Exampleembodiments include a mast orientation apparatus, which uses proximityswitches to monitor the position (in 90° increments, or four specific“orientations”) of the grapple. Within the nuclear reactor industry inthe U.S., these four orientations may be sometimes referred to asorientations 1, 2, 3 and 4 (foreign plants may refer to them as 0, 1, 2and 3). Alternatively, the orientations may be referred to as easy left,hard left, easy right, and hard right. The Permissive Control Systemprovides a mast orientation signal, indicating which “orientation” (1,2, 3 or 4) the mast and grapple are in, that may be relayed back to aPLC (programmable logic controller) cabinet. Other inputs to the PLC mayinclude the plant coordinates (x-axis and y-axis location) of the mast.The PLC may then provide grapple orientation and mast location to anindustrial computer, personal computer (PC), operator touch-screen orother such user interface, described generically as a “computer”throughout the remainder of the specification. Alternatively, theorientation and location information may bypass the PLC and go directlyto the computer. The computer may provide user interface information,including orientation and location, to a user that may be located forinstance on a refueling platform. The PLC and or computer may provideuser input related to the movement of reactor components. Such input maybe entered piecemeal, in a pseudo-manual or semi-automatic mode, oralternatively input data related to component movement (pick-up anddrop-off locations and orientations of components, and the sequence ofcomponent movements) may be pre-programmed such that the computer/PLCcan operate in more of an automatic mode.

The computer may provide a user interface related to reactor componentmovement, which may then be relayed to a PLC that in turn controls mastmovement, in x-axis and y-axis locations throughout the plant. The PLCmay also control the z-axis movement of the grapple by controlling thetelescoping nature of the mast. The PLC examines the orientation(rotation) of the grapple and mast, and may then prohibit the z-axismovement of the mast into the reactor core or the spent fuel pool.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of example embodiments willbecome more apparent by describing in detail example embodiments withreference to the attached drawings. The accompanying drawings areintended to depict example embodiments and should not be interpreted tolimit the intended scope of the claims. The accompanying drawings arenot to be considered as drawn to scale unless explicitly noted.

FIG. 1 is a overhead view of fuel cells located in a nuclear reactorcore;

FIG. 2 is an overhead view of fuel cells, with a single fuel assemblyremoved from one of the fuel cells;

FIG. 3 is an overhead view of fuel cells, with two fuel assemblies(positioned diagonally from each other) removed from one of the fuelcells;

FIG. 4 is an overhead view of fuel cells, with a double blade guideplaced in the empty positions of two fuel assemblies that have beenremoved from a fuel cell;

FIG. 5 is an overhead view of fuel cells, with a double blade guideplaced in the empty positions of two fuel assemblies of a fuel cell, anda third fuel assembly removed from the fuel cell;

FIG. 6 is an overhead view of all four fuel assemblies being removedfrom a fuel cell, with a double blade guide positioned in the emptypositions of two diagonally opposed fuel assemblies;

FIG. 7 is an elevation view of a conventional telescoping mast andgrapple, with a mast orientation apparatus added to the top of the mast;

FIG. 8 is an overhead view of the top of the mast orientation apparatus;

FIG. 9 is a depiction of a telescoping mast and grapple located above areactor component, and a refueling platform supporting a PLC cabinet andcomputer user interface;

FIG. 10 is a flowchart of an example embodiment of the PermissiveControl System computer program, in an automatic mode; and

FIG. 11 is a flowchart of an example embodiment in a semiautomatic mode.

DETAILED DESCRIPTION

Detailed example embodiments are disclosed herein. However, specificstructural and functional details disclosed herein are merelyrepresentative for purposes of describing example embodiments. Exampleembodiments may, however, be embodied in many alternate forms and shouldnot be construed as limited to only the embodiments set forth herein.

Accordingly, while example embodiments are capable of variousmodifications and alternative forms, embodiments thereof are shown byway of example in the drawings and will herein be described in detail.It should be understood, however, that there is no intent to limitexample embodiments to the particular forms disclosed, but to thecontrary, example embodiments are to cover all modifications,equivalents, and alternatives falling within the scope of exampleembodiments. Like numbers refer to like elements throughout thedescription of the figures.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it may be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between”, “adjacent” versus “directlyadjacent”, etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising,”, “includes” and/or “including”, when usedherein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

Referring to FIG. 1, a nuclear reactor core 105 may be composed ofindividual fuel assemblies or bundles 104 located in a single quadrantof a fuel cell 102. Fuel cells 102 are generally square in shape, andcontribute to an overall matrix-like appearance of the core 105. Fuelcells are replaced, during a plant refueling outage, by first removingeach of the four fuel assemblies of a fuel cell, as depicted in FIGS. 1through 6.

Referring to FIG. 2, during a typical plant refueling outage, one offuel assemblies 104 is removed, leaving a temporarily vacant fuel cellquadrant 110.

Referring to FIG. 3, it is common practice to remove and then replaceentire fuel cells by first removing a fuel assembly 104 from a fuel cellquadrant 110, and then removing the diagonally opposing fuel assembly104, leaving a diagonally opposing vacant fuel cell quadrant 112.

Referring to FIG. 4, a double blade guide 114 may then be placed in thediagonally opposing vacant areas 110 and 112 of the fuel cell, in orderto ensure that the remaining fuel assemblies 104 in fuel cell quadrants115 and 117 located near the vacant quadrants 110 and 112, aresupported, such that they stay in a vertical position.

Referring to FIG. 5, another fuel assembly 104 may be removed leavinganother vacant quadrant 117 of the fuel cell 102.

Referring to FIG. 6, the final fuel assembly 104 of the fuel cell 102may be removed leaving the vacant quadrant 115. The fuel cell 102 withall empty quadrants, quadrant 110, 112, 115 and 117, is now be ready forinspection and or later refueling (by placing new fuel assemblies 104 inthe fuel cell 102, or moving partially used fuel assemblies from otherareas of the core to the fuel cell 102).

Referring to FIG. 7, a conventional telescoping mast 70 and fuel grapple72 may be outfitted with a mast orientation apparatus 71, according toan embodiment of the present invention. While not shown, theconventional mast and grapple generally includes a motor-driven bridge(for x-axis movement of the mast) and trolley (for y-axis movement),manually operated mast rotation, a motor-driven hoisting cable forelevation changes (z-axis movement) of the mast, pneumaticallycontrolled opening and closing of the fuel grapple, a controller thatmay be programmed to position the mast (via the bridge and trolley) atspecific plant coordinates, and a display screen or graphical userinterface to notify the user of the location (coordinate) and elevationof the mast and the open/closed position of the grapple. The mastorientation apparatus 71 may monitor and indicate the orientation (angleof rotation) of the mast and grapple, as it is being manually rotated ina conventional manner. In one embodiment, such orientations may beassigned in 90° increments. For instance, the mast and grapple may be ata position assigned to be 0°, 90°, 180°, or 270°. The motor-drivenbridge and trolley and the conventional controller associated with thebridge/trolley may be operated in a conventional manner to position themast for pick-up or drop-off of components, although example embodimentsprovide for the controlled movement of the mast in either automatic orsemi-automatic mode (shown in FIGS. 10 and 11) with a graphical userinterface and PLC (156 and 151, of FIG. 9) displaying the location ofthe mast and further control component movements. Sensing of the mastand grapple location may be accomplished by conventional means, as themast and grapple location (plant coordinate) are calibrated,conventionally, based on the location of the bridge and trolley, andthis location may be transmitted to a PLC, computer, controller, orother such means of controlling the mast and grapple location as a partof the Permissive Control System. The Permissive Control System maycontrol the motor-driven hoisting via the PLC (151 of FIG. 9), whileexample embodiments allow a user to view the elevation of the fuelgrapple on a graphical user interface (156 of FIG. 9). The PermissiveControl System may control the pneumatic opening and closing of the fuelgrapple via the PLC (151 of FIG. 9), while example embodiments allow theuser to view the open or closed status of the grapple on a graphicaluser interface (156 of FIG. 9). The Permissive Control System mayprohibit a change in the position of the grapple (either from open toclosed, or closed to open) unless the mast and grapple are at arequested plant location, elevation and orientation. The conventionaldisplay screen or graphical user interface (156 of FIG. 9) may be usedwith the Permissive Control System, with example embodiments providingthe user with information pertaining to the physical location(coordinate) of the mast, the elevation of the fuel grapple, the open orclosed status of the fuel grapple and the orientation of the mast.

The mast orientation apparatus 71 may include a trolley mounting plate78 that supports a gimbal bearing 74. The gimbal bearing 74 supports agimbal plate 76 that may be allowed to freely rotate on top of thegimbal bearing 74. As the mast 70 and grapple 72 rotate about an axis ofrotation 73 in order to adjust orientation, the trolley mounting plate78 and the gimbal bearing 74 remain approximately stationary, and atleast a portion of the gimbal plate 76 rotates with the mast 70 andgrapple 72 in order to mirror the grapple 72 orientation. A cam (or,target) 80 may be positioned on top of the gimbal plate 76, such thatthe cam 80 rotates with the rotation of the gimbal plate 76. Proximityswitches 82 may be located on the trolley mounting plate 78, orotherwise located along the periphery of the gimbal plate 76. As the cam80 rotates on top of the gimbal plate 76, the position of the cam 80 ismonitored by the proximity switches 82. Proximity switches 82 may be anytype of proximity switch/sensor, limit switch reed switch, or similartype of device that may sense the relative position of the cam 80. Theproximity switches 82 may be biased, such that when several proximityswitches 82 are used, the switches may accurately recognize which switch82 the cam 80 is closest to at any given time.

Referring to FIG. 8, a top view of the mast orientation apparatus 71depicts the trolley mounting plate 78 that supports a gimbal plate outerrace 76 b. The gimbal plate outer race 76 b in turn supports a gimbalplate inner race 76 a. A cam 80 is affixed to the gimbal plate innerrace 76 a. The cam 80 and gimbal plate inner race 76 a mirror rotationof the mast 70 and grapple 72 (FIG. 7), while the gimbal plate outerrace 76 b may remain approximately stationary relative to the mast 70and grapple 72 (FIG. 7) rotation. Proximity switches 82 may be locatedalong the periphery of the gimbal plate outer race 76 b, such that theproximity switches 82 may detect the position of the cam 80, as thegimbal plate inner race 76 a and cam 80 rotate relative to the trolleymounting plate 78 and gimbal plate outer race 76 b.

Referring to FIG. 9, a conventional mast 70 and grapple 72 may beoutfitted with a mast orientation apparatus 71. A user 154, such as acore engineer, may view operation of the mast 70 and grapple 72 from arefueling platform 158. The mast orientation apparatus 71 may generate amast orientation signal 200 that may be transmitted to a PLC(programmable logic controller) cabinet 151, that receives theorientation signal 200 along with the other information such as thephysical location of the mast 70 or the elevation of the grapple 72. ThePLC 151 may then generate a location/orientation signal 202 to a userinterface display such as an industrial computer, touch-screen, or apersonal computer (computer) 156. The computer 156 may allow the user154 to view the location (physical coordinate) of the mast 70, theelevation of the grapple 72 (as the mast 70 telescopes and contracts),and the orientation (angle of rotation) of the grapple 72 as the grapple72 rotates about an axis of rotation 73. The computer 156 allows theuser to enter the pick-up coordinate 150 and drop-off coordinates 152 ofreactor components, either prior to or during the movement of reactorcomponents.

The computer 156 may generate a control signal 204 that may betransmitted to the PLC 151, describing the desired movement of the mast70 and grapple 72. The PLC 151 may then generate a mast control signal208 that may be transmitted to a motor (not explicitly shown) of themast 70 and grapple 72, in order to control the x-axis, y-axis, z-axismovement of the mast 70 and the open and closed position of the grapple72.

Computer 156 may be programmed, via a computer program, to control thelocation of the mast and act as a permissive for the opening/closing andelevation of the fuel grapple, in an automatic, semi-automatic, or amanual mode. FIG. 10 provides a description of an example embodimentpertaining to an automatic type mode. Referring to FIG. 10, themast/grapple may be controlled through the use of the Permissive ControlSystem computer program, by a user manually selecting an AUTOMATIC modein step S2 on a touch-screen or computer, causing the mast to move to apre-programmed pick-up coordinate S4. It should be appreciated that inAUTOMATIC mode, the pick-up and drop-off coordinates of all reactorcomponents may already be pre-programmed into a computer 156 or PLC 151(depicted in FIG. 9) prior to a user selecting AUTOMATIC mode in stepS2. The pick-up and drop-off coordinates and component orientations maymatch a move sheet, conventionally used to describe the movements ofreactor components during plant refueling or start-up. It should beappreciated that the pre-programmed pick-up and drop-off information mayinclude the sequencing of these movements, such that a pre-programmedorder in which the components may be moved exists.

Once the mast moves into place above a reactor component, but prior tothe grapple being allowed to enter a user-programmable elevation (forinstance, 6 inches) above the top guide of the core or above the top ofthe spent fuel rack, the Permissive Control System verifies that theactual mast and grapple coordinate and orientation matches the requestedcoordinate and orientation in step S24. If the mast/grapple are not inthe correct coordinate/orientation, the Permissive Control Systemprohibits the grapple from being lowered in step S28 and provides anerror signal in step S28 to notify the user that the mast/grapple may beout of position. If the mast/grapple are in the properlocation/orientation in step S26, the Permissive Control System maypermit the user to manually lower the grapple to the elevation of thereactor component in step S6 for pick-up. It should be appreciated thatdue to the physical constraints of a tightly bundled reactor core orspent fuel pool, the Permissive Control System does not permit rotationof the mast/grapple once the grapple moves below the user-programmableelevation above the top guide of the core or above the top of the spentfuel pool, as a reactor component attached to the grapple could strikeor damage surrounding equipment if allowed to rotate during componentinsertion or extraction. Furthermore, between the point where acomponent may be picked-up and prior to being dropped-off (i.e., duringthe time when the grapple may be carrying a component), the PermissiveControl System may take into account the length of the component itself,such that the user-programmable elevation above the core or spent fuelpool will then take into consideration that the grapple may be carryinga component, of given length, that may not be allowed to strike ordamage equipment that is located below such pre-programmable elevation.

Example embodiments provide the Permissive Control System with a systemRESET in step S10, at any instance when: 1) the grapple cable is slack(i.e., the grapple cable may be at rest, as opposed to being taught asin the case where the grapple may be carrying a component or otherwisesuspended above a component before or after component pick-up ordrop-off), and 2) the grapple hooks change position (i.e., change fromopen to closed, or closed to open). It should also be noted that thesystems permissive control related to any specific step in a pick-up ordrop-off sequence (for instance, a permissive control that is notallowing the grapple to be manually raised, because the grapple wasnever closed during pick-up) may be manually bypassed (i.e.,, the systemis RESET) by either turning off the Permissive Control System.Additionally, example embodiments allow the system to automaticallyRESET if an ERROR message occurs (this may be the case when the mast ismoved to a pick-up or drop-off, but the location or orientation of themast/grapple does not match a requested location/orientation) or if aMANUAL operation mode is entered.

When the user manually closes the grapple in step S8 in order to pick-upa component, the system then assumes that, in this instance, a componenthas been picked-up, in step 10. Example embodiments of the PermissiveControl System may refer to this as a system RESET, as the system isoperating under the assumption that the manual closing of the fuelgrapple in step S8 indicates that the grapple is now carrying acomponent, as indicated in step S11. The system then permits a user tomanually raise the grapple in step S12.

A user may automatically move the mast to a pre-programmed destination(drop-off) coordinate by making a manual selection that may be availableon a user interface, in step S14. Example embodiments may optionallyinclude a selection labeled “INCREMENT” (shown in step S14) on a userinterface that may be manually selected to accomplish such automatedmovement of the mast. When the mast reaches the drop-off point, thesystem then verifies that the actual mast/grapple coordinate andorientation match a requested coordinate and orientation in step S25.The system determines whether the mast/grapple is properlylocated/oriented in step S27, and if they are not, then the grapple maybe prohibited from being lowered in step S28 and an error signal may beprovided for a user in step S28 in order to signify that the mast and/orgrapple are not in a correct location/orientation for componentdrop-off. If the mast/grapple are correctly located/oriented, then auser may be permitted to manually lower the grapple in step S16 forcomponent drop-off. Once the user has manually lowered the component,the system permits the user to manually open the grapple in step S18, tocomplete component drop-off. Once the grapple is manually opened, thesystem may automatically RESET in step S28, as the system considers thecomponent to have been dropped-off in step S29. The user may be thenpermitted to manually raise the grapple in step S20. The user may selectINCREMENT in step S22, and the mast may be then automatically relocatedto the next pre-programmed location S4, in order to pick-up the nextcomponent in the pre-programmed sequence of reactor component movements.

It should be appreciated that one of the benefits of AUTOMATIC mode maybe the preprogrammed nature of the reactor component locations and thesequence of component movements. However, due to the sheer magnitude ofcomponents needing to be moved during plant refueling or startup, it maybe inevitable that such a sequence of component movements may becomemore quickly accomplished by partially deviating from the exact sequenceinitially programmed into the computer or PLC at the outset of componentmovements. Therefore, the Permissive Control System may be capable ofallowing components to be picked up and dropped-off in an order thatdiffers from the originally planned reactor engineer move sheet, whilestill ensuring that each individual component may be picked-up anddropped-off in the proper location/orientation.

FIG. 11 provides a description of an example embodiment pertaining to asemi-automatic or pseudo-manual type mode. Referring to FIG. 11, themast/grapple may be controlled through the use of the Permissive ControlSystem computer program, in a semi-automatic or pseudo-manual mode, by auser manually selecting SEMI-AUTOMATIC mode in step S30. A user thenenters, via a computer 156 (FIG. 9) or other user interface, a pick-upcoordinate and orientation for a reactor component in step S32. A userthen manually verifies that the entered pick-up coordinate/orientationmay be correct in step S34 before making a manual selection that causesthe mast to automatically move to the entered pick-up coordinate in stepS36. Example embodiments may optionally include a selection labeled“AUTO-RUN” (shown in step S36) on a user interface that may be manuallyselected to accomplish such automated movement of the mast.

Once the mast comes to rest above the entered pickup coordinate, thePermissive Control System verifies that the actualcoordinate/orientation of the mast and grapple match the requestedcoordinate/orientation in step S49. The system determines if the propergrapple coordinate/orientation exists in step S51, and if it does not,the Permissive Control System then prohibits the grapple from beinglowered in step S58 and an error signal may be provided for a user instep S58 to signify that the grapple coordinate or orientation may beincorrect. If the Permissive Control System determines that the grappleis at the proper coordinate or orientation, then the user is permittedto manually lower the grapple to the elevation of the component in stepS38.

Once the grapple is lowered to the component, the user may be permittedto manually close the grapple in step S40 in order to pick-up thereactor component. At this point, the Permissive Control System may beRESET in step S42, as the system considers the component to have beenpicked-up in step S53. The user may be then permitted to manually raisethe grapple in step S44.

While still in SEMI-AUTOMATIC MODE, the user then manually enters adestination (drop-off) location in step S46. The user may make a manualselection that allows the mast to automatically move to the drop-offdestination in step S48. Example embodiments may optionally include aselection labeled “INCREMENT” (show in step S48) on a user interfacethat may be manually selected to accomplish such automated movement ofthe mast. Once the mast comes to rest above the destination coordinate,the Permissive Control System may then verify that the mast and grappleare at a coordinate and in an orientation that matches therequested/entered coordinate and orientation in step S55. The systemdetermines if the proper coordinate/orientation exists in step S56, andif the mast/grapple is not be in the proper coordinate or orientation,then the grapple is prohibited from being lowered in step S58 and anERROR signal may be provided in step S58 to notify the user that themast/grapple is not in the proper location or orientation for drop-off.If the mast/grapple is in the proper location/orientation, then a useris permitted to manually lower the grapple in step S50 for componentdrop-off. Once the grapple lowers the component to a resting elevation,the user may be permitted to manually open the grapple in step S52. Thesystem may then RESET in step S57 as the Permissive Control Systemconsiders the component to have been dropped-off in step S59.

The user may then be permitted to manually raise the grapple in stepS54, and enter a new pick-up coordinate for another component in stepS32.

It should be recognized that many similarities between AUTOMATIC mode(FIG. 10) and SEMI-AUTOMATIC mode (FIG. 11) exist, with the differencelying in the fact that in SEMI-AUTOMATIC mode the user may input pick-upand drop-off coordinates and orientations while the process is ongoing,as opposed to entering the coordinates/orientations and sequencing ofcomponent movement upfront as a part of the AUTOMATIC mode process.SEMI-AUTOMATIC mode could be considered a pseudo-manual mode. In a trulyMANUAL mode of operation, where a user may be given total control tomove and rotate the mast and grapple, the Permissive Control System maybe entirely disengaged, such that the system does not provide any errorsignals or prohibit the movement of the grapple or mast during thepotential movement of components. In a truly MANUAL mode of operation, asystem interface may provide a user indication to indicate that thePermissive Control System is not active, such that the user may movecomponents generally at their own risk, with no guidance or verificationfrom the Permissive Control System.

Example embodiments having thus been described, it will be obvious thatthe same may be varied in many ways. Such variations are not to beregarded as a departure from the intended spirit and scope of exampleembodiments, and all such modifications as would be obvious to oneskilled in the art are intended to be included within the scope of thefollowing claims.

1. A mast orientation sensing apparatus, comprising: a gimbal plate, thegimbal plate configured to rotate in unison and in response to anangular rotation of a mast with a grapple on an end of the mast; a camattached to the gimbal plate, the cam, the gimbal plate, the mast andthe grapple configured to rotate bi-directionally and in a samedirection with each other; a plurality of switches positioned inproximity to the gimbal plate, the switches configured to detect aposition of the cam; a controller configured to determine an orientationof the mast and grapple based on the detected position of the came. 2.The mast orientation apparatus of claim 1, wherein the plurality ofswitches include four switches located at substantially 90 degrees ofangular separation from each other.
 3. The mast orientation apparatus ofclaim 1, wherein the switches comprise limit switches, proximityswitches, reed switches, or other such switches configured to detect thepresence of the cam.
 4. The mast orientation apparatus of claim 3,wherein the switches are biased so that only the switch located nearestthe cam may indicate the cam position.
 5. A mast orientation system,comprising: the mast orientation sensing apparatus of claim 1, a sensorconfigured to sense a location of the mast and grapple; the controllerconfigured to receive the sensed location, the controller configured toprohibit a lowering of the mast and grapple if the sensed location andorientation do not match a requested location and orientation
 6. Thesystem of claim 5, further comprising: a user interface configured todisplay the mast and grapple location, orientation, and a grappleposition, the grapple position being either opened or closed.
 7. Thesystem of claim 6, wherein the controller is further configured toprohibit a changing of the grapple position, from either opened toclosed or closed to opened, if the controller detects that the sensedlocation and orientation of the mast and grapple are not in therequested location and orientation.
 8. The system of claim 6, whereinthe user interface is configured to allow a user to input the requestedlocations and orientations, the requested locations and orientationscorresponding to pick-up and drop-off locations and orientations ofreactor components.
 9. The system of claim 8, wherein the user interfaceis configured to allow a user to input a sequential order of reactorcomponent movements, the sequential order corresponding to the movementof reactor components on a nuclear reactor move-sheet.